Abstract
In this study, a two-stage fluidized-bed gasification system was used to determine the distribution of heavy metal contaminants in simulative waste and evaluate the effect of the bed operating temperature, Equivalence ratio (ER), and Steam/Biomass ratio (S/B) in stage 1. The heavy metal concentrations in bed materials and fly ash were measured in two stages. The results show that as the operating temperature of stage 1 increased, the quantity of heavy metals entrapped by stage 1 bed material decreased, while that captured by stage 2 bed material increased. The less volatile Cu was mostly entrapped in stage 1 bed material. The ER and S/B results show that increasing the ER and S/B caused a slight increase in the concentrations of heavy metals entrapped in stage 1 and stage 2 bed materials. However, the influences of ER and S/B were less than that of temperature. The major factors affecting the heavy metal distribution were the operating temperature and the heavy metal volatility. Stage 2 bed material was able to entrap gaseous heavy metals or particles containing heavy metals by particle filtration and chemical adsorption. Thus, the heavy metals (Cu and Pb) had a downward trend after passing through stage 2.
Highlights
Taiwan produces about 750 million metric tons of municipal solid waste (MSW) every year.The two predominant methods for MSW treatment are recycling and incineration
Simulative waste was mainly composed of wood chips and PP plastic granules wrapped with the PE plastic bag material, and 1 mL aqueous solutions of the nitrate salts of the heavy metals were added to the PE plastic bag for coating
The distribution patterns of heavy metals with the change in the Steam/Biomass ratio (S/B) were similar to those with the change in Equivalence ratio (ER): as the amount of heavy metals entrapped in stage 1 bed material decreased, the heavy metal concentrations in the stage 1 fly ash increased
Summary
Taiwan produces about 750 million metric tons of municipal solid waste (MSW) every year. The two predominant methods for MSW treatment are recycling and incineration. There are 24 large incineration plants treating over 600 million tons of waste every year in Taiwan. In order to reduce the influence of MSW incineration, the government has been actively seeking treatment methods other than just recycling resources from waste and incineration. Since most of the waste is organic matter, if the incineration treatment could be transferred to a gasification treatment of waste, can the pollution from traditional incineration plants be solved, but we can obtain reusable energy from the process. The mixture of gases obtained after gasification is called synthesis gas (syngas), and it contains mainly CO, CH4 , H2 , and other gases [1]. Syngas can be further purified and directly burned or used as raw chemical materials; this technology is a promising alternative to incineration [2]
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